The present invention relates to an IC card in which image information is formed on a surface of the base board having ICs, and more particularly relates to an IC card having image information of high quality formed by means of thermal transfer.
Conventionally, an IC card shown in FIG. 4 is well known.
In FIG. 4, numeral 1 is a base board of a plastic card on which ICs are mounted. On a surface of the base board of this IC card, character and image information 7 such as an employee's number, name of the employee, date of issue and term of validity is recorded. This character and image information 7 is protected when a transparent sheet 10 is thermally pressed on the surface of the IC card. Japanese Patent Publication Open to Public Inspection No. 4480/1992 discloses the following technique: At a point of time when information is provided, the information is recorded on the surface of the card. Then the surface is coated with ultraviolet-ray-hardening type coating by which a transparent or translucent film is formed. In this way, information can be recorded on the IC card even after the card has been manufactured.
However, according to the conventional method, the quality of information recorded on a previously manufactured IC card is not competent. For example, concerning the surface condition of an IC card, there is a difference between a portion in which the ICs are mounted and a portion in which the ICs are not mounted, with respect to the hardness, heat conductivity, thermal shrinkage factor and the like. For this reason, after the IC card has been subjected to thermal press, irregularities and unevenness are caused on the surface of the IC card, which is not appropriate for recording information.
For example, even when the surface of the IC card is flat and smooth, excellent printing characteristics can not be provided because the surface is hard. Especially when information to be recorded is a piece of image information such as a portrait photograph having gradation properties, and when the information is recorded on the IC card by means of thermal transfer, problems are caused in the image reproduction.
From the viewpoint of preventing forgery, it is necessary to competently protect information recorded on the IC card. However, according to the conventional method in which a resin layer having thermal adhesion property is thermally transferred onto the IC card, information can not be competently protected. Accordingly, there is a possibility that information is subjected to forgery. The conventional method has the above problems.